The present invention relates to a dry etching apparatus for use in the manufacture of semiconductors, thin film devices, etc.
Since such devices as referred to above have been increasingly miniaturized in recent years, severe requirements are demanded for a dry etching apparatus. For example, high dimensional accuracy, high anisotropic properties, high selectivity for a resist, an undercoating film or the like, etc. must be provided. In one device, the temperature of a wafer during etching has been controlled with good accuracy in an attempt to maintain the wafer at a low temperature.
An example of a conventional dry etching apparatus will be described below.
Referring to FIG. 4, there is shown a reaction chamber 1 of a conventional dry etching apparatus which can be kept under a vacuum. A lower electrode 2 for holding a base material 4 is connected to a high frequency power source 7. A thin insulating layer 3 is provided on the upper surface of the lower electrode 2 as in contact with the entire rear surface of the to-be-processed base material 4. An upper electrode 6 is grounded and is provided with a reaction gas entrance (not shown). Reference numeral 5 designates an insulating spacer.
Generally, the lower electrode 2 is made of aluminum and the insulating layer 3 is formed of hard aluminum obtained by anodizing aluminum, having a thickness of 20-80 .mu.m.
The lower electrode 2 is shown in detail in FIGS. 5A and 5B. Referring to FIGS. 5A and 5B, reference numerals 8 and 9 designate a path along which cooling water flows to cool the base material 4 and a push-up mechanism to push the base material 4 upward so as to transfer the base material 4, respectively. When the push-up mechanism 9 is moved up and down, the base material 4 is lowered onto the lower electrode 2 or is lifted up and then transferred.
The operation of the dry etching apparatus having the above-described structure will now be described.
A reaction gas is introduced in the reaction chamber 1 and the reaction chamber is placed under a desired degree of vacuum. As the high frequency power is supplied from the high frequency power source 7, plasma is generated and the base material 4 is etched. At this time, the base material 4 has a minus potential (approximately -500 V--1500 V) corresponding to the decreasing voltage of the cathode because of the plasma. Since the lower electrode 2 is covered with the insulating layer 3, a direct current potential is O V. Therefore, the base material 4 and the lower electrode 2 constitute the electrodes of a capacitor with the insulating layer 3 interposed therebetween, and the impression of the voltage to the capacitor brings about an electrostatic attraction force. As a result of this, the base material 4 is tightly adhered to the insulating layer 3 by the lower electrode 2. Accordingly, a good thermal conduction is achieved, and the temperature of the base material 4 becomes close to that of the lower electrode 2, thus making it possible to process the base material 4 at low temperatures.
In one example, when a 6-inch wafer is processed for one minute with O.sub.2 gas, at 150 mTorr pressure, under 300 W of high frequency power at 13.56 MHz, and with a 100 mm distance between electrodes 2 and 6 while the lower electrode 2 is at 20.degree. C., the temperature of the wafer after the electrostatic attraction is 40.degree. C. Without the electrostatic attraction, that is, when the insulating layer 3 is not provided, the wafer is at 120.degree. C.
In the above structure, the minus charges stored in the base material 4 remain even after the power source 7 is turned OFF. Therefore, the electrostatic attraction continues, causing the base material 4 to leap and shift when the push-up mechanism 9 pushes the base material 4 upward as shown by dotted lines I and II in FIG. 5B. The base material 4 is not smoothly handed over to a transfer arm which, in the worst case, results in the base material 4 being broken.
Although the output of the high frequency power source 7 can be lowered before the transfer of the base material 4 so as to decrease the charging potential of the base material 4 or N.sub.2 gas can be blown in order to reduce the residual attraction force, it is hard to completely remove the residual attraction force.